Field of the Invention
The present invention relates to a fuel system that is mounted on an aircraft or the like.
Description of the Related Art
A wing box provided in aircraft is used as a fuel tank. The wing box extends along substantially the entire length of a main wing, and a fuselage. An inner portion of the wing box is divided into a plurality of fuel tanks as described in Japanese Patent Laid-Open No. 08-40394.
It is assumed that the plurality of fuel tanks include two fuel tanks of an outer tank (a first tank) that is provided in the main wing, and an inner tank (a second tank) that is provided in a root portion of the main wing and the fuselage.
In this configuration, there are a case in which a pump is provided in each of the fuel tanks, and fuel is supplied to an engine from both the fuel tanks, and a case in which a pump is provided only in one of the fuel tanks, and fuel is supplied to an engine from the fuel tank. In the latter case, the fuel is transferred from one of the fuel tanks to the other of the fuel tanks as described in Japanese Patent Laid-Open No. 08-40394.
In view of efficiently supporting the fuel by lift that the main wing receives, it is generally preferable that more fuel is stored in the outer tank than in the inner tank, and the fuel in the inner tank is consumed before the fuel in the outer tank.
In this case, a case in which the fuel is supplied to the engine from both the outer tank and the inner tank (referred to as the former case below), and a case in which the fuel is supplied to the engine only from the outer tank (referred to as the latter case below) are described.
In the former case, a fuel supply pump 18 that pumps the fuel toward the engine, and a valve (not shown) are provided in each of an outer tank 15 and an inner tank 16 as shown in FIG. 14A. The operations of the respective fuel supply pumps 18 and 18 and the valves are electrically controlled based on the fuel amounts in the respective tanks 15 and 16 detected by sensors such that the fuel in the inner tank 16 is reduced first.
In the latter case, the fuel supply pump 18 that pumps the fuel toward the engine is provided in the outer tank 15, and a transfer pump 19 that transfers the fuel from the inner tank 16 to the outer tank 15 is also provided as shown in FIG. 14B. Control as described below is performed. That is, the transfer pump 19 is started, and a valve provided together with the transfer pump 19 is opened to start fuel transfer when the fuel amount in the outer tank 15 falls below a predetermined amount by detecting the fuel amount in the outer tank 15 by a sensor. When the fuel amount in the outer tank 15 reaches a full amount, the transfer pump 19 is stopped, and the valve is closed.
In any of the former and the latter cases, it is necessary to construct a complicated system that electrically controls the pump and the valve.
Thus, the number of necessary members, such as a sensor and a control unit, is increased. From the perspective of decreasing the weight, the cost, and the possibility of failure, the number of members provided in an airframe is desired to be reduced as much as possible.
Particularly, in middle-sized and small-sized aircraft having a smaller airframe than large-sized aircraft, there is a more demand for a decrease in the number of members in view of a space to install the sensor and the control unit.
Based on the above problems, an object of the present invention is to provide a fuel system which achieves, with simple and a small number of members, a configuration in which fuel in a second tank is consumed before fuel in a first tank, that is, the amount of fuel stored in the second tank is reduced before the amount of fuel stored in the first tank.